CNID data is sent from a telephone company central office over a standard telephone line to the subscriber. This data is sent as a burst of Bell 202 1200 baud asynchronous data between the first and second occurrence of ringing voltage. The most common CNID device marketed to subscribers is a free-standing LED or LCD display unit. This unit provides a display of the data and perhaps a limited storage of incoming call data. However, these units provide no means to export the data or of easily preventing the caller's telephone number from being transmitted.
A CNID device that attaches between the CNID telephone line and a PC's serial or parallel port is also currently available. This device demodulates the CNID Bell 202 data and sends it into the PC for further processing. However, this device does not collect and store information while the PC is turned off. Nor does this device allow for the dialing of the telephone number with or without a blocking prefix.
Occasionally the calling party may not want the called party to receive their telephone number. Most central office systems provide a means to block transmission of the calling party on a per-call basis through a CNID blocking prefix. However, prior to the present invention, activating this blocking feature was cumbersome and required the repeated dialing of additional digits for each blocked call. Additionally, if the calling party is serviced by a PBX, the blocking code's position depends on the type of call. In short, prior to the present invention automatic insertion or removal of the CNID blocking prefix in the number stream was not possible.
Therefore it is the objective of the present invention to provide an automatic way of insertion and removal of CNID blocking prefixes into a telephone number in a computer based telephone management system.